One of the more preferred methods of controlling weeds in crops involves the post-emergent control of weeds wherein herbicide(s) are applied after the crop in question has emerged from the soil. Post-emergent control is desirable as it requires the application of herbicide only where an infestation of weeds is present. In contrast, pre-emergent control requires the application of herbicide early in the growing season before most weeds have germinated, with the result that such chemicals must be employed throughout a field even if they would ultimately not be needed.
There are approximately 20 million acres of canola grown in western Canada. At harvest canola crops leave an average of 2-3 bushels per acre of seed in the field, or at least 20 times the normal seeding rate. Canola seed can remain viable in the soil for 2 to 3 years, and with shortened crop rotations, volunteer canola has become a major weed pest in crops, including canola crops.
Bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), is an effective post-emergent herbicide for a number of weeds, particularly broadleaf weeds, including volunteer canola.
Protoporphyrinogen oxidase (PPO) is an enzyme found in both plants and animals, which is responsible for the seventh step in the biosynthesis of protoporphyrin IX. This porphyrin is the biosynthetic precursor of hemoglobin in animals and chlorophyll in plants. The enzyme catalyzes the dehydrogenation of protoporphyrinogen IX to form protoporphyrin IX.
Protoporphyrinogen oxidase inhibitors are herbicides that act by blocking the production of chlorophyll and heme in a plant, causing an accumulation of protoporphyrinogen IX that is ultimately toxic to the plant.
A majority of the canola planted in Canada and the USA has been genetically modified to be tolerant to glyphosate or glufosinate. Therefore these herbicides, when used as a burn down treatment on a field prior to seeding with canola seed, fail to control canola weeds. A solution to this problem is described herein.